Revieivs — Summary of Progress for 19'20. 473 



that some geologists are incdined to regard evidence of oil 

 impregnation in a desert country as equivalent to genuine seepages 

 in moister regions. The whole question is discussed in a scientific 

 manner with reference to transport, presence of reservoir- and cap- 

 rocks, domal structures (of which a list is given), and faults. The 

 authors conclude hy specifying, as requested, two localities which 

 they regard as slightly more favourable for test-wells than any of 

 the others. 



J. J. H. Teall. 



Summary of Pkogress of the Geological Survey for 1920. 



Mem. Geol. Survey, pp. v+112, 3 figs. 1921. Price 3s. 6rf. 

 rPHE Summary of Progress of the Geological Survey for the year 

 1920 records the work of the Survey for the first year under the 

 Directorship of Dr. J. S. Flett, under whom its high standard of 

 efficiency will no doubt be maintained. 



In order to accelerate the revision of the maps in the coalfield areas, 

 reorganization of the field units has been made and the staff expanded 

 accordingly. The plan of decentralization will no doubt allow the 

 work and experience of the oflicers of the Survey to be utilized more 

 completely by the public as a whole, since they will be more 

 accessible for consultation on the spot at the local offices. 



Field work has been carried out in all the districts where work 

 was in hand before the war. Perhaps the most interesting results 

 achieved are those in the English Midlands and the West Highland 

 District of Scotland. In the Midland area the Silurian rocks afford 

 fresh evidence of Jones' contention that the so-called Upper 

 Llandovery represents the sandy facies of the Tarannon, in which 

 case it is not surprising that the Tarannon Shales have been looked 

 for in vain. The close agreement of the higher beds with those of the 

 typical Ludlow area is also of interest. With regard to the latest 

 glacial deposits, significant features are the occurrence of sands and 

 gravels deposited as a series of fans which mark the successive 

 stages of the ice front instead of terminal moraines. 



In the AVest Highlands the completion of the mapping of Mull 

 foreshadows the publication of the eagerly awaited memoir on that 

 area. Detailed work in lona has revealed the existence of a platform 

 of Lewisian Gneiss overlain by Torridonian sediments. The Archean 

 complex is very varied, and appears to include both the ortho- 

 and paragneisses and a group of schists composed in part of highly 

 altered sediments, of which the well-known lona marble is one. 

 Of special interest are the pegmatites, which are quite unfoliated, 

 and therefore later than the metamorphism and the shearing 

 movements. 



On the palseontological side by far the most significant feature of 

 the year's work is the discovery of an undoubted Rhaetic faima 

 in beds at Grubin, Mull, where for the first time Rhaetic beds in situ 

 are recognized in Scotland. 



